Bimetallic switch cutout



July 19, 1966 P. H. J. BROUWER 3,251,947

BIMETALLIC SWITCH CUTOUT Filed July 27. 1964 2 Sheets-Sheet l FIG. 3

s 20 4 13 4 1 11 12 8 9 Z J L f i INVENTOR.

PIh'TER H.-J.' BRD WEK July 19, 1966 P. H. J. BROUWER 3,261,947

BIMETALLIC SWITCH CUTOUT Filed July 27. 1964 2 Sheets-Sheet 2 INVENTOR. P/ETEA H .7. BRouwu BY j ZM E. AGE/VT.

United States Patent 3,261,947 BIMETALLIC SWITCH CUTOUT Pieter Hendrik Johannes Brouwer, Drachten, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed July 27, 1964, Ser. No. 385,152 5 Claims. (Cl. 200-113) The invention relates to a bimetal switch including a bimetallic strip and a resilient moving switch element, which each are mounted at one end on a support which contains the fixed contact, the bimetallic strip holding the moving element against spring action in a locked position in which the moving element engages the fixed contact, the locked condition being removed when the bimetallic strip is curved to a certain extent by heating.

In known devices of this kind the bimetallic strip and the moving switch elements are arranged so as to interlock in a position in which the switch is closed. Thus, two moving elements are interlocked, but this provides difficulty inter alia with respect to the reproducible determination of the temperature at which unlocking occurs. In addition, in the known devices the said components generally are curved so that they occupy a comparatively large amount of space and furthermore with respect to the above-mentioned requirement of accurate reproducible operation the curved form causes difficulty in manufacturing and mounting.

It is the object of the present invention to obviate the said disadvantages and the invention is characterized in that the moving switch element comprises a leaf spring which is subjected to an initial stress and, in the locked position, is enclosed in a substantially stretched condition between a bimetallic strip in a substantially stretched condition and a flat support to which the bimetallic strip is directly locked, the said components extending substantially side by side in the longitudinal direction.

This provides the advantage of a fiat bimetallic-strip switch, which consequently occupies little space, and this is of importance because such devices frequently are to be used in locations where only little space is available. However, a higher degree of accuracy with respect to the unlocking temperature is also obtained, inter alia owing to the fact that the bimetallic strip is directly locked to the support, and hence any difference in the unlocking temperature in different devices becomes so small as to permit to dispense with the provision of a separate adjusting mechanism to enable the locking to be adjusted after mounting.

The use of components in the stretched condition as the moving switch element and the bimetallic strip is known. In such devices the bimetallic strip is interposed between a resilient moving switch element and the support, the moving element being raised from the fixed contact owing to the curvature of the bimetallic strip produced by heating. In most cases, this raising movement is slow so that arcing occurs and the contact points are burned.

An advantageous embodiment is characterized in that the bimetallic strip is locked behind a locking member rigidly secured to the support, while the application of heat moves the bimetallic strip from a locked position to a position in which by the curvature of the strip its effective length is reduced to an extent such that it is just free from the locking member.

This provides the advantage that the locking member also may have a slight height, because the unlocking movement is performed in the longitudinal direction of the support. Furthermore the locking member may be comparatively robust, because due to the curving of the bimetallic strip at its centre the unlocking forces may be reduced to tensile forces which greatly exceed the bending forces of the strip.

A preferred embodiment is characterized in that a cylindrical locking pin is secured to the free end of the bimetallic strip substantially at right angles to the plane of the strip, the said pin passing through an aperture in the resilient moving switch element and being provided with a laterally projecting head or collar which in the locked condition engages a locking plate secured to the support.

This provides a simple construction of the unlocking member, the locking pin being rigidly secured to the bimetallic strip and hence when the strip is flexed performing a slight tipping movement, which facilitates unlocking. This also permits of a favourable embodiment in which the aperture in the support through which a rivet is passed which looks the bimetallic strip and the moving switch element, is slit-shaped. Consequently, before the final riveting it may simply be ensured that the locking pin engages the edge of the locking plate, so that the accuracy of the locked position and hence the differences in the unlocking temperature in different switches are kept within narrow limits. '7

The invention and several additional details to be used to advantage will now be described fully with reference to an embodiment given, by way of example, in the accompanying drawings, in which:

FIGURE 1 is a longitudinal sectional view of the switch in the locked condition,

FIGURE 2 is a side elevation of the switch in the open condition,

FIGURE 3 is a plan view of the switch of FIGURE 2,

FIGURE 4 is a plan view similar to FIGURE 3 with the omission of part of the upper component, and

FIGURE 5 is a sectional view of a device in which the bimetallic strip switch is included as a protection against excessive temperatures. 1

Referring now to the figures, a rigid support 1 of insulating material in the form of a short strip is provided at its ends with holes 2 and 3. A leaf spring 4 is provided at its end with a corresponding hole 5 and is secured to the support 1 with the aid of a hollow rivet 6. Beyond the end of the support 1, the spring 4 is bent downward into the form of a contact slip 7. The spring 4 extends along the surface of the support 1. The free end of the spring 4 makes contact with the end of a short contact plate 8 which is provided with a hole and is secured to the other end of the support with the aid of a hollow rivet 9. The end of the plate 8 is slightly bent upward along the support. Beyond the end of the support 1 the other end is bent downward into the form of a second contact clip 10. However, the spring 4 is subjected to an initial stress such that in its free condition it is inclined upward with respect to the support and hence is to be pressed down to make contact with the plate 8. Near its free end the spring is provided with an aperture 11 while the remaining material on both sides of the aperture is bent into the form of a lug 12.

A bimetallic strip 13 at one end, which is provided with a hole 14, is secured to the support 1 with the aid of the rivet 6, a washer 14 being interposed between the spring and the bimetallic strip, The bimetallic strip 13 extends along the support 1 and the leaf spring 4 and has about the same length as this spring. It is of advantage for the bimetallic strip to be disposed on the outside of the switch so that it may readily absorb heat. If the heat transfer is substantially effected by radiation, the other surface of the bimetallic strip may advantageously be coated with carbon black, which considerably accelerates the heat transfer. A pin 15 is secured to the bimetallic strip near the end thereof so as to extend downwardly at right angles to the plane of the strip. This pin comprises a cylindrical body 16 which has a narrow part 17 and terminates in a collar 18 the diameter of which is greater than that of the narrow part. The collar 13 has a slightly tapering end face 19. Near the fixed end of the bimetallic strip 13 a notch 20 and 21 respectively in the form of a semi-circle is provided in each lateral edge, the narrow part between the notches 20 and 21 being provided with a score 22 at right angles to the longitudinal direction of the strip 13, and along this score the strip is bent upward through a small angle (FIGURE 2). Beyond the location of the pin 15 another transverse score 23 is made, along which the end part 24 of the strip is bent through a small angle. In the free condition (FIGURE 2) the bimetallic strip 13 extends upwardly with respect to the support 1 similarly to the spring 4, with the difference that the strip is not curved but is made up of straight portions.

The rivet 9 also serves for securing a locking plate 25 to the lower surface of the support opposite the contact plate 8. An edge 26 of the plate 25 projects beyond the edge of an aperture 27 provided in the support 1. The aperture 11 in the spring 4 and the aperture 27 are situated in line so as to permit the pin 15 to pass through them when the bimetallic strip 13 is moved towards the support, for example, with the aid of a pressure stud 28.

In FIGURE the bimetallic strip switch is mounted in the housing of a fan heater. The push-button 28 is arranged above the end part 24. When the push-button 28 is operated, assuming the bimetallic strip switch to be in the free condition (FIGURE 2), the bimetallic strip 13 is moved downward and, after the pin 15 has passed through the aperture 11 in the spring 4, the spring follows this downward movement, the lug 12 engaging the bimetallic strip in a manner such that the axis of the pin 15 and the upper edge of the lug 12 lie in one plane. Subsequently the pin 15 enters the aperture 27 of the support 1. In this position the spring 4 is depressed through a distance such that its free end makes contact with the plate 8. Furthermore the tapering end face 19 engages the edge 26 of the locking plate 25. When the button is pushed slightly further, the end of the bimetallic strip and hence the pin 15 perform a slight tipping movement about the lug 12, which is promoted by the engagement of the tapering face 19 with the edge 26, and subse quently the collar 18 of the pin 15 snaps being the edge 26. Thus the switch is locked.

In the embodiment shown in FIGURE 5 the switch is clamped onto .a switch panel 29, the clips 7 and making electric contact with connecting terminals 30 and 31. As a result the switch is connected in a circuit which includes a helical heating wire, a few turns of which are shown schematically by 32. When the heating current is switched on, the ambient temperature causes the bimetallic strip 13 to curve upwardly owing to the reduction in width caused by the notches 20 and 21. As a result, the distance between the pin and the rivet 6 is decreased. At a predetermined temperature this distance becomes so small that the pin 15 is disengaged from the locking plate 25 with a quick snap (FIGURE 1). The spring 4 then breaks the contact. When the bimetallic strip 13 has cooled down and consequently is again in the stretched condition, the switch may again be closed with the aid of the push-button 28.

The switch need not be adjustable since it may readily and accurately be adjusted during mounting.

The temperature at which unlocking occurs is determined by the distance between the wall of the narrow portion 17 and the outer edge of the collar 18 of the pin 15. When the switch is being mounted and is adjusted it must only be ensured that in the stretched condition of the bimetallic strip the edge 26 of the unlocking plate 25 engages the wall of the narrow portion 17. For this purpose the aperture 2 in the support 1 has the form of a slit so that before final riveting the bimetallic strip may be slightly shifted longitudinally with respect to the support.

What is claimed is:

1. A bimetallic switch cutout comprising .an elongated support having a fixed contact adjacent one end, a similarly elongated bimetallic strip and leaf spring, means connecting one end of each said strip and spring on said support in overlapping spaced relation, said spring being stressed for elevating the other end of said strip and spring above said contact, a locking pin adjacent said one end, said locking pin being connected with said strip, an aperture in said spring, said locking pin extending freely through said spring aperture and projecting beyond said spring, a collar on said pin at said projecting end, and means connected with said support for latching with said collar upon movement of said strip and spring into position adjacent said support and in engagement with said contact; movement of said bimetallic strip unlocking said pin upon reaching a determined temperature whereby said contact is reopened.

2. A bimetallic switch cutout according to claim 1 wherein said bimetallic strip is laterally notched at both edges adjacent said one end.

3. A bimetallic switch cutout according to claim 2 wherein said bimetallic strip is bent through a small angle away from said support, said bend being located on a lateral line joining said notches and substantially normal to the longitudinal axis of said strip.

4. A bimetallic switch cutout according to claim 1 wherein said leaf spring has a reverse bend adjacent said spring aperture, said reverse bend supporting said strip.

5. A bimetallic switch cutout according to claim 1 wherein said means for connecting said strip and spring to said support comprises rivet means, said support having a longitudinally elongated aperture for receiving said rivet, said elongated aperture allowing adjusting movement of said strip and spring relative to said fixed contact.

References (Iited by the Examiner UNITED STATES PATENTS Re. 17,840 10/1930 Sandin 200-116 1,925,781 9/1933 Taylor 200--122 2,025,525 12/1935 Pittman et al. 2001l6 2,175,341 10/1939 Clark 200122 FOREIGN PATENTS 680,127 7/ 1939 Germany.

BERNARD A. GILHEANY, Primary Examiner.

L. A. WRIGHT, Assistant Examiner. 

1. A BIMETALLIC SWITCH CUTOUT COMPRISING AN ELONGATED SUPPORT HAVING A FIXED CONTACT ADJACENT ONE END, A SIMILARLY ELONGATED BIMETALLIC STRIP AND LEAF SPRING, MEANS CONNECTING ONE END OF EACH SAID STRIP AND SPRING ON SAID SUPPORT IN OVERLAPPING SPACE RELATION, SAID SPRING BEING STRESSED FOR ELEVATING THE OTHER END OF SAID STRIP AND SPRING ABOVE SAID CONTACT, A LOCKING PIN ADJACENT SAID ONE END, SAID LOCKING PIN BEING CONNECTED WITH SAID STRIP, AN APERTURE IN SAID SPRING, SAID LOCKING PIN EXTENDING FREELY THROUGH SAID SPRING APERTURE AND PROJECTING BEYOND SAID SPRING, A COLLAR ON SAID PIN AT SAID PROJECTING END, AND MEANS CONNECTED WITH SAID SUPPORT FOR LATCHING WITH SAID COLLAR UPON MOVEMENT OF SAID STRIP AND SPRING INTO POSITION ADJACENT SAID SUPPORT AND IN ENGAGEMENT WITH SAID CONTACT; MOVEMENT OF SAID BIMETALLIC STRIP UNLOCKING SAID PIN UPON REACHING A DETERMINED TEMPERATURE WHEREBY SAID CONTACT IS REOPENED. 